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Microsoft Corp. is working with the OPC Foundation to enable almost any IIoT scenario using interoperability between the millions of OPC UA-compliant applications and equipment. Microsoft will enable IIoT users to connect manufacturing equipment and software with extended support of OPC UA's open-source software stack. Microsoft’s extended support for OPC UA spans its IoT offerings from local connectivity with Windows devices to cloud connectivity via Microsoft Azure. Integration with Azure IoT allows customers to easily send OPC UA data to the Azure cloud, as well as command and control OPC UA devices remotely from the Azure cloud.
Pepperl+Fuchs broke ground June 2 on its new U.S. distribution and engineering center in Katy, Texas, near…

While routine build-up and clogging in process applications is annoying, process scaling is more persistent, causes unplanned downtime and increases costs in many industries. It's typically composed of calcium carbonate, wax, grease or similar…

Just as you can't have too many friends, level measurement applications can't get enough ease of use, reliability and safety. Thanks to increasing process industry needs and user demand for them, these are the three unifying priorities that drove…

Our panel of experts explore best practices for dealing with buildup on chemical seals of a differential pressure flowmeter.

Q: We have a venturi flowmeter with 3-in. flanged pressure taps and flanged chemical seals with capillary tubes in a 44-in. vertical pipe (Figure 1). The fluid is hydrocarbon (polymeric) gas. The problem is that the chemical seal diaphragms often…

A Control Design reader writes: We have several temperature, pressure and flow sensors on a new medical-device cleaning skid that we are developing. These instruments are connected to a PLC as 4-20 mA inputs, and there is also a 4-20 mA output used to control a pump motor speed. A recent failure of a flow sensor brought the process skid instrumentation to my company's quality manager's attention. He asked how we know that the temperatures, pressure and flow are accurate, and how do we know that we are cleaning properly.
I've been tasked to write a procedure for troubleshooting, calibrating and testing the 4-20 mA instruments on the skid. I can probably stumble through this, but what are some best practices for troubleshooting the analog…

Control's Monthly Resource Guide brings you the latest online resources on a variety of process control topics.

MULTI-PART WEIGHING
This four-section webpage by Omega Engineering covers "Weighing Applications," "Weighing System Design," "Installation and Calibration" and "Specialized Installations." The whole group is located at…

FOPDT model has demonstrated utility for controller tuning rules, for structuring decouplers and feedforward control algorithms.

A first-order plus deadtime (FOPDT) model is a simple approximation of the dynamic response (the transient or time-response) of a process variable to an influence. It’s also called first-order lag plus deadtime (FOLPDT), or “deadtime” may be…

'To the degree networks and standards can provide easy, consistent and seamless access to device-resident controls, the vision of truly distributed control may finally dawn upon us.'

Every compressor in the facility went down at once that day, when a PLC redundancy switchover didn’t transfer in time. The engineers didn’t know that each P453 remote I/O processor had a dip-switch-selectable timeout setting—if it didn’t…

A Control Design reader writes: We have several temperature, pressure and flow sensors on a new medical-device cleaning skid that we are developing. These instruments are connected to a PLC as 4-20 mA inputs, and there is also a 4-20 mA output used to control a pump motor speed. A recent failure of a flow sensor brought the process skid instrumentation to my company's quality manager's attention. He asked how we know that the temperatures, pressure and flow are accurate, and how do we know that we are cleaning properly.
I've been tasked to write a procedure for troubleshooting, calibrating and testing the 4-20 mA instruments on the skid. I can probably stumble through this, but what are some best practices for troubleshooting the analog…

Most public utilities deliver basic power and water, and God bless them for doing it. However, a few go beyond their essential missions, and seek to further enhance the overall well-being and prosperity of their communities.
One of these is…

Advanced control on fuel and steam can control emissions while saving millions.

It’s no secret that advanced process control (APC) has played a major role in the process industries for many decades. However, while many organizations focus only on major process units, there’s often an untapped opportunity to do more, and…

Our readers tell us who they think delivers the best technology in our industry

There's knowledge in our readers. That's why every year we ask our loyal audience to help us determine which automation service providers offer the best products and brands they can rely on to get the best combination of performance, ease of use,…

Just when it seems like today’s sophisticated motors and drives can’t possibly add more efficiencies and capabilities, engineers conjure up new tricks and refinements, followed by end users and system integrators who materialize new settings and…

Control's monthly guide brings you invaluable industry information to stay up to date on the latest trends and developments.

THE CLASSIC VALVE BOOK
The fourth edition of the 295-page classic text, "Control Valve Handbook," by Fisher Controls International and Emerson Process Management reports this classic text has been a primary reference since its first printing in1965.

Control's monthly guide brings you invaluable industry information to stay up to date on the latest trends and developments.

THE CLASSIC VALVE BOOK
The fourth edition of the 295-page classic text, "Control Valve Handbook," by Fisher Controls International and Emerson Process Management reports this classic text has been a primary reference since its first printing in1965.

Just when it seems like today’s sophisticated motors and drives can’t possibly add more efficiencies and capabilities, engineers conjure up new tricks and refinements, followed by end users and system integrators who materialize new settings and…

Actionable information is essential for the effectiveness of the 'loop,' as it is for closed-loop control and open-loop alarms.

When I sat down in my office this morning, I was greeted by the operations manager, who pointed out an entry from last night’s operations log: “Did you see? The boiler steam vent is in manual because the pressure reading whacked out and made the…

Actionable information is essential for the effectiveness of the 'loop,' as it is for closed-loop control and open-loop alarms.

When I sat down in my office this morning, I was greeted by the operations manager, who pointed out an entry from last night’s operations log: “Did you see? The boiler steam vent is in manual because the pressure reading whacked out and made the…

Actionable information is essential for the effectiveness of the 'loop,' as it is for closed-loop control and open-loop alarms.

When I sat down in my office this morning, I was greeted by the operations manager, who pointed out an entry from last night’s operations log: “Did you see? The boiler steam vent is in manual because the pressure reading whacked out and made the…

Our readers tell us who they think delivers the best technology in our industry

There's knowledge in our readers. That's why every year we ask our loyal audience to help us determine which automation service providers offer the best products and brands they can rely on to get the best combination of performance, ease of use,…

Visualizing and contextualizing safety data can have a positive impact on productivity and compliance.

"Information is one thing, but safety information is quite another," says George Schuster. He should know. He’s charged with business development for the Global Safety Team of Rockwell Automation and has seen many plants and factories begin to…

How to deal with the constraints of putting access points in hazardous areas.

In an ideal world, it wouldn’t be necessary to worry about explosive atmospheres. Unfortunately, plant environments are far from ideal, with most process plants being about 80% Class I, Div. 2 (Zone 2) and another 10% Class I Div. 1 (Zone 1), so…

Key is to learn as much as possible to make digital technologies safe, secure and successful in process settings.

As usual, and I’m sure this is true for many of you, this year’s autumn season has been a frantic dash of work, deadlines, sleep deprivation, indigestion and suspiciously arthritic stiffness. In my case, this means covering all sides of the…

With today’s network technology, even Ethernet and wireless are almost always fast enough.

As automation professionals, one issue we have about control loops is ensuring we're able to support real-time control. Historically, when Ethernet was 10 MB/s and there were multiple drops on a single port, collisions were a significant concern and…

With today’s network technology, even Ethernet and wireless are almost always fast enough.

As automation professionals, one issue we have about control loops is ensuring we're able to support real-time control. Historically, when Ethernet was 10 MB/s and there were multiple drops on a single port, collisions were a significant concern and…

Because they're the crossroads, nexus and Grand Central Station for sensor signals and data arriving and requests and actuation instructions departing, it's a big help that I/O and terminal blocks are more flexible and capable than ever.

Compact, Remote I/O for Zone 2/Div 2
LB System remote I/O has more power in less space with high-performance, compact modules plugged into a backplane. Energy-saving power management and low-power dissipation allow maximum packing density. With the…

Be just 33 seconds more productive each hour, and the savings mount quickly.

Rockwell Automation previewed its new, forward-looking App Platform for mobility at this week’s TechED conference in Orlando. While focused first on redefining smartphone use on the plant floor – with the aim of making individual workers more…

Control’s latest State of Technology report delves into the many aspects of power systems of interest in process plants.

From sourcing and ensuring uninterrupted flows of clean electricity to monitoring, regulating and metering generation and consumption throughout a facility, process automation professionals who want a smooth-running, efficient and reliable facility are well advised to seek and control power.
This anthology of recent articles delves into the many aspects of power systems of interest in process plants. Remote and wireless systems are speeding development and standardization of energy harvesting and improved battery systems.
Line-powered supplies that used to only transform electricity and maybe offer surge protection are now monitoring and measuring current and voltage profiles, implementing alerts and alarms, and sending data up to…

Greg: Here we take advantage of the chance to talk to Bill Thomas, who provides a great lesson of how to succeed in advancing capabilities and opportunities in his career and the control systems for which he was responsible. His career and the…

Control's monthly guide brings you invaluable industry information to stay up to date on the latest trends and developments.

AT THEIR BEST, ALL THE TIME
ExperTune’s white paper, “How to Improve Performance of Process Control Assets,” by George Buckbee, P.E., describes the practice of real-time asset performance management, shows how to get assets to perform at their best all the time, and demonstrates the value of integrating these tools for a performance picture that delivers financial results. It’s available here.
ISA / www.isa.org
ANALYZING, PREDICTING PROBLEMS
This 57-minute video, “Avoid Equipment Surprises: Predictive Diagnostics for Oil & Gas,” is presented by Joe Dupree, GE Automation and Controls, and users from NiSource Gas and Alyeska. They demonstrate condition-based monitoring, predictive analytics and other tools for evaluating…

Steve Christian remembers the days—not too long ago—when production schedules were printed on sheets of paper and distributed to operators at his plant, who would manually twist valve handles to send the Ragu sauce tomato slurry from one kettle…

Advanced control on fuel and steam can control emissions while saving millions.

It’s no secret that advanced process control (APC) has played a major role in the process industries for many decades. However, while many organizations focus only on major process units, there’s often an untapped opportunity to do more, and…

Find and slay the dragons lurking in the typical safety instrumented system.

Cybersecurity is a growing concern in the process industries, and a number of good articles have been written about it for industrial control systems (ICS)—many full of doom and gloom. Here, we will divide the ICS into two parts: safety…

Big data can only help users if they understand what it is, how it can affect their controls and processes, and how they can use it to optimize operations.

Similar to any new technology emerging on the process control front, big data can only help users make better decisions if they understand what it is, how it can affect their controls and processes, and how they can use it to optimize operations.

Our readers tell us who they think delivers the best technology in our industry

There's knowledge in our readers. That's why every year we ask our loyal audience to help us determine which automation service providers offer the best products and brands they can rely on to get the best combination of performance, ease of use,…

Three alternative approaches to better loop control

What's wrong with those ramps? Well, as the performance of control loops declines over time, there are better alternatives to properly handle potential problems. Check out what to avoid when tuning your ramps.

IN TODAY'S controllers, ramping block devices are widespread in most DCSes and PLCs as a built in feature. This consists of either ramping the setpoint from one operating point to another production rate, or limiting the rate of change of the controller output through a ramp. Most of the time, when people intend to use a ramp device, they attempt to:

Avoid overshooting during a setpoint change

Respect equipment constraints such as electrical (over-current), thermal or mechanical stress or

Make the transition from one operating point to another smoother.

For any of these three approaches, there is a better alternative to properly handle those potential problems.

Avoiding Overshooting During a Setpoint Change Wherever the ramp is located – either at the controller output or at the setpoint – there will certainly be an overshoot for a non-self-regulating process and a high potential of overshoot for a self-regulating process (higher potential for Lag dominant process model) according to the tuning’s aggressiveness (See Figure 1 below). This is what we see by looking at G2(s), G3(s) and G5(s): all of them are overshot. On the other hand, G1(s), which was step changed through a Lead/Lag filter, not only is overshot, but it reached the new setpoint faster with exactly the same tuning. Consequently, the ramp will postpone the setpoint response and make it overshot. Thus, the first statement that leads people to use ramp, happens to be unjustified for both self-regulating and non-self-regulating process types.

FIGURE 1: CONTROLLING ERROR

Performances based on a simulation for a self-regulating and non-self-regulating process model. A ramped SP versus a step changed SP going through a Lead/Lag filter has been applied.

WHAT IS THIS Lead/Lag filter? This function is often available as a built-in device in most DCSes and PLCs on the market. It consists of a ratio between 0 and 1 of two time constants. One of them is the numerator and acts as the leader. The leader corresponds to the instantaneous portion of the step change applied to the controller. For instance, if the ratio is 0.7 then 70% of the step is instant or abrupt change and the other 30% is going through a first order filter, which is also called Lag.

The denominator is the lag, which is actually the time constant of a first order filter. Generally, this filter time constant will match the tuning value of the integral action in the controller. This type of mechanism will give you the best of the two worlds: no overshoot during setpoint change and fast load rejection.

Because of this Lead/Lag filter, tuning can be optimized for load disturbances without having any overshoot at all during a setpoint change. Furthermore, the load rejection will remain the fastest it can get during a load disturbance. Without a Lead/Lag filter, most people’s natural tendency is to relax the tuning to avoid overshooting too much on a set point change, or to use a ramp and get an overshoot of different magnitude depending on the tuning’s aggressiveness.

When using a Lead/Lag filter, the excitation signal sent to the PID controller has a sharp break at the beginning, then the rest of the pattern is very smooth. In fact, it has the same shape as a first order response. When using the ramp pattern, there are two abrupt changes: there is one at the beginning and a second one at the end when it reaches the new setpoint. The idea of a Lead/Lag function is to make a steep change at the beginning, when it is far away from the final value, then reduce the speed for the final approach. A two-degree of freedom PID controller (Integral only on SP change) will produce similar results.

The settling time can be improved by a factor of two without overshoot when using a Lead/Lag filter. Settling time is defined as the time that has passed for both the Process Value and Controller Output to reach steady state and remain within the range of a normal process noise.

The settling time is cut by a factor of two when using a Lead/Lag filter, as opposed to using a ramp applied on the set point or using a ramp limiter applied at the controller output where this latter acts as a slew rate limiter.

In addition to lengthening the settling time by 100%, the ramp caused (in this example) an overshoot of 10%. If the aggressiveness of the tuning and the slope of the ramp are reduced to lessen the overshoot as much as possible to the minimum, then the settling time could be increased by a factor as high as four, which is a considerable amount. Consequently, with a ramp, the reduction of the overshoot during a set point change implies a significant increase of the settling time. On the opposite, the Lead/Lag filter does not create overshoot for both types of process, that is to say self-regulating and non-self-regulating.

Respecting Equipment Constraints For the second solution, which is intended to protect the equipment from being stressed, over-used or broken, there is a more appropriate approach to solve this issue than using a ramp limiter at the PID output. For instance, if the cause of the stress is brought about by a high heat flow rate phenomenon, then another controller could be acting as an override or constraint controller on the temperature differential between the two surfaces or two points. A constraint controller will override the valve through a low-select signal block. Since the stress from the heat is proportional to the heat flow, which is a consequence of the temperature differential between the two points, this constraint controller will take over by just the appropriate amount of output correction and avoid causing stress.

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